For Crysis Warhead:
1) Download Both Crysis & Crysis Warhead
2) Open the folder where Crysis Warhead is installed
3) You'll see a Bin32 folder and a Bin64 folder
4) Delete the Bin32 folder
5) Rename the Bin64 folder to Bin32
6) Open the new Bin32 folder
7) Delete the "Crysis" application
8) Rename the "Crysis64" application to just "Crysis"
9) Crysis Warhead Now Works!

For Crysis:
1) Right click and copy that new Bin32 folder you made for Crysis Warhead
2) Paste it into the Crysis install file (replace the old "Bin32" file with the new one from Crysis Warhead.
3) Crysis Now Works!

METHOD 2)

I Haven't Tested This But This Should (But It's NOT Guaranteed) To Work